Safety electrical connection



y 1950 A. H. LEJA 2,507,723

SAFETY ELECTRICAL CONNECTION Filed Nov. 25, 1946 Patented May 16, 1950UNITED STATES PATENT OFFICE 9 Claims.

This invention relates to safe electrical connections for electricappliance cords and more particularly to plug connections of therenewable cord type.

The present invention combines several features of improvement overpreviously known plugs of related types.

One object of the present invention concerns an improvement throughwhich separable parts of a plug body of novel form. are locked in safelyassembled relation by the cord when in use.

Another objectconcerns provision, of an improved solderless connectionbetween an. insulation sheathed, expandable conductor and anotherelectrical conductor, in which the two conductors are pressed into firmcontact by elastic strain in the insulating sheath.

A still further object is tocombine anv improved solderless electricalconnection held under compression between parts of a housing, withsafety locking structure assuring that the connection will not becomeloosened or exposed during use.

The invention having the above objects, and additional objects andadvantages which may appear in this specification, can be carried intopractical effect as described below with reference to the accompanyingdrawing, in which like reference characters have been employed toindicate similar parts throughout the several views.

Fig. l of the drawing is an isometric view of an assembled safety plugconnection according to the invention;

Fig. 2 is an exploded view" of the plug connection shown in Fig. 1,showing the several parts in position for assembly;

' Fig; 3 is an isometric View of a partial assembly of parts of the plugshown in Fig. 1;

Fig. 4 is an exploded view similar to; Fig. 2' of a modified form ofplug connection according to the invention;

Fig. 5 is a view", similar to; Fig. 3,, of a partial assembly of theyparts of the modified plug, connection of Fig. 4';

Fig. 6 isa plan view of an assembled plug connection of. the modifiedform shown in Fig. 4;

' Fig. 7 is a cross sectional view taken on the line VII-VII of Fig. 6;

Fig. 8 is a longitudinal section of a second modified plug connectionembodying the: invention taken. on line: VIII,--VIII of Fig. 10;

Fig. 9 is an end elevation of the plug, connection of Fig. 3 with aportion broken away; and

Fig. 101s a front elevation. of the modified form of plug connectionshown in. Fig. 8.

, In-the. embodiments of the invention illustra ed in the, drawing, aunique type of electrical connection has been employed. For reasons ofsimplicity it is highly desirable, in a plug connection of thereplaceable type, to be able to make connection between the insulatedconductors of an electrical fixture cord and the contact fingers of theplug connection, without removal of any of the cord insulation, andwithout the use of tools. The present invention provides such aconnection.

In the present invention, electrical contact pieces such as the plugcontact fingers I, generally of the type used in plugs for homeappliances, are provided with transversely ridged, or threaded, prongs2, tapered to a point, similar to the ordinary wool screw; Prongs 2 maybe inserted endwise among the strands of a flexible stranded conductor 3having a more or less resilient covering of insulation 4, withoutremoving or disturbing the insulating covering in any way. The act ofinsertion of the tapered prong 2 among the strands of the conductor 3will result in an expansion of the conductor, and of the insulatingsheath 4 surrounding the same. If the portion of the conductorsurrounding the inserted prong 2 is confined laterally between surfaceswhich resist expansion of the insulating sheath 4, the insulating sheathwill be compressed between the strands of conductor 3 and such surface;and a compressional stress in the material of the insulating sheath willresult, which will exert a pressure tending to force the strands of theconductor firmly into electrical contact making relation with the prong2. This pressure will tend to deform the strands of conductor 3 withrespect to the ridges or threads of the prong 2, in such a mannerthatthere will be a strong mechanical resistance to withdrawal of the prong2 from conductor 3 by relative longitudinal, translational, movement.The compressional stress in the insulating sheath 4 will also result ina lateral pressure of the sheath against the restraining surfaces,creating a frictional resistance against movement of the insulatingsheath relative to such restraining surfaces. It will be readilyunderstood that a, good electrical connection between the strands ofconductor 3 and prong 2v of contact I will be maintained by the elasticstresses in the insulating sheath 4, and that, at the same time, astrong frictional resistance against separation of the component partsof. the connection will also be maintained by the same elastic stress.

The electricalconnection described in the foregoing paragraph isemployed to practical advantage. in. a preferred form of safety plugcon- 3 struction as illustrated in Figs. 1-3. The assembly shown in Fig.1 consists of a plug body 6, a pair of contact fingers I equipped withprongs 2, a cap member I and a flexible electric cord consisting of twoflexible conductors 3, each sheathed with insulation 4.

The plug body member 6, as illustrated in Figs. l-3, consists of a thickdisk, or short cylinder, of a suitably rigid insulating material, suchas, for example, one of the common, so-called plastic or synthetic resinmaterials. Other materials,

such as glass, ceramics and other compositions may obviously be used.The disk or cylinder 6 is pierced by two suitably shaped apertures 8,through which the contact fingers I may be extended. The base ends ofcontact fingers I, from which the prongs 2 extend, are suitably formedso that the contact fingers may not pass entirely through the apertures8. When the contact fingers are inserted in operative relation to bodymember 6, the prongs 2 will extend in laterally spaced parallel relationto an endsurface 9 of the member 6, which will be referred tohereinafter as the rear end surface of such body member. This rear endsurface of body member 6 may be provided with a raised boss 9a betweenthe apertures 8, such boss having lateral surfaces in spaced parallelrelation to prongs 2 of contact fingers I when the same are in assembledrelation thereto. A third aperture or passage I I extends from the rearthrough the front surface of body member 6, and opens also through thecylindrical, peripheral surface thereof, for reasons to be describedhereinafter. Passage H, in the illustrated embodiments, takes the formof an axially extending groove in the peripheral surface of plug body 6.A groove II a across the front of disk 6 may also form a part of passageII for reasons described hereinafter. The'body member 6 is externallythreaded for engagement with the cap member I. Cap member I has aninternally threaded, hollow, cylindrical portion, or annular flange I2,adapted to threadedly engage body member 6, and to peripherally surroundthe body member when fully engaged therewith. The can thu has acylindrical recess open only at one end, through the flat front faceformed by the edge of flange I2. Cap member I and body member 6, whenfully engaged, enclose a cavity between the rear end surface of bodymember 6 and the internal surface of cap I, for a reason describedhereinafter, the inner surface of cap 1 having portions opposed to therear end surface of body member 6. A lock slot, or notch I3 is formed inthe annular flange I2 of cap 1, opening through the edge of the flange,as shown in Figs. 1 and 2, for a purpose described hereinbelow.

In assembling the safety plug connection of the present invention, apair of contact fingers I are connected with the unstripped ends of apair of flexible, insulated, cord conductors 3, by

insertion of the prongs 2 among the strands of the conductors. In thecase of threaded prongs, this may be accomplished by manually insertingthe point of the prong endwise among the conductor strands, and rotatingthe same as an ordinary wood screw, the rotation resultin in an axialadvance of the prong, relative to the conductor strands, in the samemanner as a wood screw will advance into a piece of wood. Afterconnection of the contact fingers I with the cord conductor tips, thecontact fingers I are inserted in apertures 8 and the flexible cordconductors are flexed so that the standing parts pass through passage oraperture I I and through the front end surface of the body member 6, asclearly i1- lustrated in the partial assembly of Fig. 3. With theconductors in this position, cap I is threadedl engaged with body member6 and rotated, relatively thereto, until the flange I2 fully engages andsurrounds the threaded peripheral surface of the body member 6. As thecap 1 approaches full engagement with body 6, the internal surface ofcap I approaches the rear end surface of body 6 in such a manner as toengage the insulated ends of conductors 3 just prior to reaching alimiting position of full engagement. It will be clearly understood thatthe elastic sheath of insulation 4 surrounding the prongs 2 will becompressed between opposed surface portions of the body member 6 and capI, so that when the cap "I is fully engaged with body 6, portions of theinsulating sheath 4 will be under compression between the expandedconductor 3 and the engaged surface portions of plug body 6 and cap I.The elastic stresses in the insulating sheath l will-exert pressurestending to maintain electrical andmechanical connection between theprong 2 and the strands of conductor 3, and frictional engagementbetween the sheath 4 and engaged portions of the rear end surface of theplug body 6 and internal surface of cap I. When the cap I and plug body6 are thus fully engaged, it will be seen that contact fingers I will befirmly held in place with relation to the plug body 6 and that theelectrical connection between the contact fingers and the conductors 3will be fully enclosed in the space between cap I and body member 6.

The lock slot I3, more than one of which may be provided, at angularlyspaced intervals if desired, will be so placed that it will registerwith the lateral opening of passage II through the peripheral surface ofbody member 6 when the plug and body are substantially fully engaged byrelative rotation. The cap member I may now be firmly locked in place byflexing the conductors 3 so that their standing parts extend radiallyoutward from passage II, through lock slot I3. In order that somelatitude may be allowed for as to the final tightness of the assemblywithout providing a plurality of lock slots, groove Ila across the faceof body 6 may be used to accommodate the standing part of the cord whenpassage I I is turned past, or short of register with lock slot I3.

It will be seen, as illustrated in Fig. 3, that portions of theconductors 3 must protrude from the front end surface of plug body 6 inorder to permit assembly and disassembly of cap I relative to the plugbody. The protruding cord portions will interfere with the insertion ofthe contact fingers I into full engagement with a cooperating socketfixture, so long as they so protrude, since the front end face of thebody member 6 should engage the external insulating face of the usualmating socket fixture, when the connection is made. Thus, the act offlexing the conductors 3 so as to pass radially through the lock slot I3is an act necessary to condition the plug connection of the inventionfor operative engagement with a mating socket fixture. And it will beseen that the same act causes a locking of the cap 1 against rotationrelative to the body member 6. The locking action results from the factthat any relative rotation of the cap and body, when so locked, willcause the conductor to be stressed in shear between surfaces of thepasage II (or groove II'a)'and lock slot I 3. This locking action is of'double importance, since it positively prevents any relative movement ofcap I and body member 6 which would tend to release the pressure on theconnection between conductor 3- and prong 2, and also will positivelyprevent removal of the cap 1 when the plug is engaged with a matingsocket fixture. The ex posed surface of the mating socket fixture willeffectively prevent any dislodgement of the conductors 3 from lock slot13- solong as the plug connection is engaged with such a mating socketfixture. Accordingly, when the plug connection of the invention isengaged in the normal manner in the ordinary type of mating socketfixture, the cap 1' will be securely locked against removal such aswould expose any live conductor.

7 The modified form of plug connection shown in Figs. 4-7 differs fromthat illustrated in Figs. 1-3 in respect to the type of threadedconnection between the body member 6 and cap 1. In the modified form,the cap 7, instead of having its flange portion [2' internally threaded,is provided with a coaxial screw projection H. The body 6' instead ofbeing externally threaded is provided with a tapped hole l6, coaxialwith its peripheral surface. The cap 1 is assembled,

relative to body member 6, by threadedly engaging screw projection M intapped hole i6, and relatively rotating the cap and body. As is clearlyillustrated, the flange I2 is formed to closely surround the peripheralsurface of body 6', so that it will be necessary to flex the conductors3 so that they will extend from the rear end surface of body 6 throughthe passage II and the front end surfaceof the body 6 as shown in Fig. 5in order to condition the parts for assembly of the cap 1' by rotationrelative to body 6'. As in the preferred form, the standing parts ofcords 3 will interfere with proper operative engagement of the plugconnection of the invention with a mating socket fixture so long as theyextend through the front surface of body member 5'. And, in order tocondition the plug for use, it will be necessary, as in the preferredform, to flex thestanding parts of the conductors so as to make themextend radially outward from passage I I through lock slot I 3, in orderthat the plug connection may be conditioned for use with a mating socketfixture.

Fig. '7 clearly illustrates the modified form of plug connection inmating engagement with a socket fixture of the usual type, the exposedinsulatingsurface of which is indicated in dotted lines at ll. Since theconstruction of such socket fixtures is well known, no illustration isbelieved necessary in this specification.

A second modified form of plug connection is illustrated in Figs. 8-10..In this form, the electrical connection of the present invention isemployed in a very simple form of cord tip plug. The plug body I 8 is asimple piece of more or less rigid. insulating material pierced by twoparallel holes IS the internal surface of which may be serrated,threaded, or otherwise roughened, if desired. A pair of contact fingers2| are provided with taper-threaded prongs 22. The simple plugconnection is assembled with relation to a pair of flexible cordconductors 3 by inserting the unstripped conductor tips into holes l9,which are of a diameter substantially equal to the normal externaldiameter of the insulation sheath conductor. The plug assembly iscompleted' by inserting the prongs 22 among the strands of conductors 3with a screwing action, which will result in an expansion of theconductors 3 and a compression of insulation sheath "4' between theexpanded conductor 3 and the internal surface of holes IS. The contact.fingers 21 are preferably locked against relative rotation by use of adouble slotted, piece of insulating material 23,. arranged to beslidaible into position against body member l8, and to fit snugly enoughto be retained in position by frictional engagement with the contactfingers 2 I. As the contact fingers 2| are rectangular, or otherwisenoncircular in cross section, thepiece 23', being slotted to fit snuglyon contact fingers 2|, Will prevent the rotation thereof relative toeach other and to body l8. As in the other forms of the presentinvention, the elastic stresses caused in insulation sheath ll, by theexpansion of conductor 3 therein while the sheath is surrounded by amore or-less rigid restraining wall, will result not only in amaintenance of a good electrical and mechanical connection between theprong 22 and the strands of conductor 3, but will also result in themaintenance of a frictional resistance against displacement of the bodymember [8 from its position surrounding the connection. The body memberl8, accordingly, will be frictionally locked in position, guarding andmaintaining the electrical connection between prongs Z2 and conductors3, :by the act of assembly. And, since non-circular contact fingers areused, the frictional locking action will prevent disassembly of the plugconnection while the contact fingers 2! are engaged with a mating socketfixture of usual type. Any attempt to pull body member I8 axially,relative to the connection between prongs 22 and conductors 3, would, ofcourse, result in pulling contact fingers 2| out of engagement with thelive socket contacts in connection with which such a plug would beemployed.

It will be understood that the elastic stress maintained electrical andmechanical connection is common to all of the fixtures describedhereinabove, and that such a connection will also be advantageous foruse in single conductor connections as well as in the ordinary twoconductor plug connection, as illustrated and described I hereinabove.It will also be understood that the body surrounding the connection neednot be absolutely rigid, but may be resilient.

While specific embodiments of the present invention are. particularlydescribed and illustrated hereinabove, such specific embodiments are byway of illustration only. It will for example be readily apparent thatthe principles involved may advantageously be employed in socketfixtures as well as plug fixtures, andv not only with strandedconductors but with all. conductors which can be expanded by insertionof a Iprong. And the present invention includes such modifications andequivalents as may occur to persons skilled in the art, within. thescope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. An electrical contact plug assembly comprising; a body of insulatingmaterial having front and rear end' surfaces and having an apertureextending therethrough; a metal contact finger extending through saidaperture from the rear through the front end surface of said body andhaving its rear end formed to prevent passa e through said aperture; aprong extending laterally from said rear end of said contact finger,tapering to a point and having: a transversely ribbed surface, thelongitudinal axis of said prong lying substantially parallel to saidrear end surface of said body acap of insulating material cooperatingwith said body to enclose the rear end surface of said body, said caphaving an internal surface portion substantially parallel to said rearend surface of said body; and interengaging means on said body and capmember, operable to move said cap member relatively to said body, in thedirection of the said rear end surface of said body.

2. A safety cord and contact plug assembly comprising; a body in theform of a cylinder of insulating material, having front and rear endsurfaces; a metal contact finger projecting from said front end surfaceand having a rear end extending through said rear end surface; aflexible insulation sheathed conductor electrically connected at one endwith said rear end of said contact finger adjacent said rear endsurface; a cap member of insulating material, coaxially threadedlyinterengaged with said body and having a cylindrical recess open at oneend only and closely fitting said body, said cap cooperating with saidbody to enclose said rear end surface and the connection between saidone end of said conductor and said rear end of said contact finger; anaxially extending groove in the cylindrical periphery of said body,capable of accommodating the portion of said sheathed conductorextending from said connection, in a manner to permit relative rotationof said cap and body to screw said body in and out of said recess duringassembly and disassembly; and a notch in the open end of said cap,through which said conductor must be extended to prevent its extendingaxially beyond said front end surface of said body when said body isfully within said recess, whereby said conductor will undisengageablylock said cap against rotation relative to said body when said plug isnormally engaged with a mating socket.

3. An electrical cord terminal fixture comprising; a cylindrical plugbody of insulating material having a contact-finger-holding apertureextending axially therethrough and a cord accommodating groovepenetrating both front and rear end surfaces and the cylindrical surfaceof said body; a cap of insulating material having a fiat front face anda recess opening in said front face, said recess being of substantiallythe same diameter as said plug body and somewhat deeper axially;coaxially threaded means on said cap and plug body interengageable byrelative rotation of said cap and plug body to draw said body into saidrecess to a position in which its front end surface is substantiallyflush with said fiat front face of said cap; and a notch in said fiatfront face of said cap, extending laterally from said recess andregisterable with said groove of said body where it penetrates saidfront end surface and the adjacent cylindrical surface of said body whensaid front end surface is substantially fiush with said flat front faceof said cap.

4. In combination with the structure of claim 3, a metal contact fingerheld in and extending through said contact finger-holding-aperture, oneend of said contact finger being exposed at said front end surface ofsaid plug body and the other end having a wood screw-threaded prongtapering to a point and extending laterally from said finger with itslongitudinal axis substantially parallel to said rear end surface ofsaid plug body and between it and the closed end of said recess of saidcap in assembly.

5. In combination with the structure of claim 4, a flexible strandedcord conductor sheathed with elastic insulating material and having one.end expanded by insertion of said screw threaded prong into its endalong its longitudinal axis and among its conducting strands within saidsheathing, said expanded end being interposed between and compressed bysaid rear end surface of said plug body and said closed end of said caprecess when said front end surface of said plug body is drawnsubstantially fiush with said flat front face of said cap, said sheathedconductor extending from said expanded end through said groove and frontend surface of said plug body to permit relative rotation in assembly ofsaid cap and plug body and being extensible laterally from said groovethrough safd notch of said cap to clear said front end surface fornormal plug use and thereby to undisengageably lock said cap againstrotation relative to said plug body when the terminal fixture is inordinary use with a mating socket.

6. An electrical contact plug assembly comprising in combination: a cordhaving multiple insulation sheathed flexible stranded conductors: aplurality of fiat-sided electrical contact fingers each having at oneend a tapered screw-threaded prong integral therewith and tapering to apoint, said contact fingers being individually connected with saidconductors by screwing said prongs endwise among and lengthwise of thestrands thereof within said sheaths of elastic insulation; and a pair ofplug parts of rigid insulating material cooperating to completely housein the prong ends of said contact fingers and. the connected ends ofsaid conductors, one of said plug parts having parallel flat-sidedapertures through which said contact fingers protrude, said one partthereby preventing disengagement of said prongs from said conductors byrelative rotation thereof.

7. An electrical contact plug assembly comprising: a cord having a pairof elastic insulation sheathed flexible stranded conductors; a pair offlat bladelike contact fingers each having at one end an integraltapered screw-threaded prong inserted by screwing endwise andlongitudinally into the end of one of said conductors within its sheathof insulation; a hollow plug part of rigid insulating material receivingand having internal surface portions flanking the ends of saidconductors into which said prongs are screwed; a second plug part ofrigid insulating material having a pair of parallel spaced slots throughwhich said contact fingers protrude in non-rotatable relation, saidsecond plug part engaging and cooperating with said hollow part to housein the connections between said prongs and conductors and to provide aninsulating holder and hand grip for the prong ends of said fingers, saidinternal surface portions of said hollow plug part serving to transmitpressure from said hollow plug part to said contact fingers and fixtheir posiitons relative to said hollow part through pressure on saidsheaths of insulation. 8. The structure of claim '7 in which said hollowplug part has the form of a block with a pair of parallel spacedapertures extending therethrough, the internal surfaces of whichconstitute said internal surface portions, and said second plug parthaving the form of a plate with said'slots alined with said apertures ofsaid block. -9. The structure of claim '7 in which said hollow plug parthas the form of a cap with a cylindrical recess and'a. notch in its openend extending laterally from said recess through the wall thereof, saidsecond plug part having the form of a cylindrical plug body of slightlyless axial length than said recess, with a longitudinal groove in itsperipheral surface, and fitting flush in the recess of said cap, saidcap and body being threadedly engaged by relative rotation, whereby saidcord must extend laterally through said notch into said groove andthrough said groove to its connection with said prongs when said plug isin use in normal engagement with a conventional outlet socket.

ALFRED H. LEJA.

REFERENCES CITED The following references are of record in the file ofthis patent:

Number Number 15 519,572

10 UNITED STATES PATENTS- Name Date Welch Jan. 21, 1913 Conklin Mar. 22,1921 Goodwin Dec. 27, 1927 Gaynor et a1 June 19, 1928 Malling Dec. 25,1928 McFadden Aug. 11, 1936 Walter May 23, 1939 Benander Aug. 13, 1940McLarn Dec. 31, 19450 FOREIGN PATENTS Country Date France Jan. 27, 1921England Dec. 3, 1925

